Quasi-impedance relay system



WITNESSES: P05 INVENTOR W fihl'rleyLGoldsbomqg/z April 1950 s. L. soLDsoRouGH 2,504,828

QUASI-IMPEDANCE RELAY SYSTEM Filed Nov. 29, 1947 7c Non-saturatizg RELAYS ATTORNEY Patented Apr. 18, 1950 UNITED STATES PATENT OFFICE QUASI-IMPEDANCE RELAY SYSTEM East Pittsburgh, Pa., Vania Application November 29, 1947, Serial No. 788,910

1 -My invention has relation to a single quasi impedance fault-detector, or pair of detectors, which is capable of taking the place of a plurality of phaseand ground-relays for responding to allkinds and combinations of faults on any of the different phases of a polyphase transmissionline. My invention also has more special rela tion to a phase-comparison, carrier-current, rotective relaying-system utilizing a pair of my new fault-detectors having diverse sensitivities.

For some years, commercial use has been made of aphase-comparing carrier-current transmission-line protective-system, the latest form of which is described and claimed in an application, Serial No. 758,200, of H. W. Lensner et al., filed June 30, 1947. In this protective system. a first overcurrent relay, of a low current-setting, was used as a fault-detector for supervising all operations affecting the phase-comparison function, and a second overcurrent relay, having a higher current-setting, was used as a less sensitive faultdetector for supervising the tripping function. This type of carrier-current protective system is not of universal applicability, because, on a two-terminal line, the more sensitive fault-de- 10 Claims.. o1.175-294) tector must be set to pick up at not less than 125% in which the minimum fault-current has been close to, or below, these values, thus limiting the application of the relay. The dimeulty just mentioned could be avoided, of course, by using standard impedance-elements, but such a course would require one relay for each phase, for both phaseand ground-faults, and this would upset the. inherent simplicity of the carrier-current protective system utilizing only a single fault-detector for taking care of all kinds and severities of phaseand ground-faults.

An object of my present invention is to provide a quasi-impedance relay which will respond to all kinds of faults, as by having an operating coil which is energized from a phase-sequence lines-current network which supplies a singlequantity which is fairly uniformly responsive to all kinds-and phases of faults, and having a restraint-coil which is energized from a minimum-- voltage network, such as that which is shown in the Harder Patent 2,393,043 granted January 15, 19%.

A further object of my invention is to provide a phase-comparison carrier-current relayingsystem, using one or two of the quasi-impedance relays just described, thus overcoming the limitation as to the minimum permissible currentsetting, without requiring any additional mechanical elements in the relay-assembly.

With the foregoing and other objects in view,

my invention consists in the systems, circuits, combinations, elements and methods of design and operation, which are hereinafter described ferred form of embodiment.

In the drawing, I have illustrated my invention as applied to one terminal of a line-section l of a B-phase transmission-line, which is connected to a 3-phase station-bus 2 by means of a circuit breaker 3 having a trip-coil TC and an auxiliary make-contact 3a. I have shown only one terminal of the protected line-section I, with the understanding that the other terminal is, or may be, a duplicate of the terminal equipment which is illustrated.

I use a bank of line-current transformers 4, which respond to the 3-phase line-current in the protected line-section I, and I supply this current to any suitable alternating-current transforming-device, network or filter, which is marked HCB, for deriving a single-phase alternating-current voltage which is applied to the primary winding of a non-saturable transformer NST. Any suitable network may be utilized, such as the network I-ICB as shown in the Harder Patent 2,183,646 of December 19, 1939, for deriving a single-phase relaying current or voltage which is reasonably uniformly responsive to a plurality of kinds and severities of phaseand ground-faults. on whatever line-phase a fault may occur. In my present invention, it is necessary or desirable, as will subsequently be explained, to use a nonsaturating network-transformer NST, or none at all, instead of the saturating transformer advocated by Harder.

The secondary winding 5 of the non-saturating transformer NST is uitilized to control two mechanical fault-detector relays FD! and FDZ, and

also to control two alternately triggering gasfilled tubes VI and V2.

In accordance with my present invention, the

two fault-detector relays FDI and FDZ are quasiimpedance relays having diverse sensitivities.

by the same designation as the relay as a whole, namely FD! and FDZ, respectively, whereas the restraint-coils have a subscript R appended thereto, thus FDIR and FDZR. Each of these relays is adjusted so that the relay will respond when the ampere-turns in its operating-coil just exceeds the ampere-turns in its restraint-coil.

The first fault-detector FDI is the more sensitive of the two relays, having a lower current setting, and a higher impedance-response, so

that it is the farther-reaching of. the. two.

The operating-coils of the two fault-detector relays PD! and FDZ are energizedin a manner which has been customary. They are shown as being energized in series with each other, from the output-terminals of a rectifier-bridge RB, which is supplied with energy from the secondary winding 5 of the non-saturating network.- transiormer NST. There are a number of different alternating-current transforming-devices or networks which are available, for providing suitable current for energizing the operating coils FD and FD2 so that these relays will be fairly uniformly responsive to all kinds of phaseand ground-faults, no matter which phase, or how i voltages, as supplied by three potential-transformers Ta, Tb and To, but I am not limited. to the phase-to-phase voltages. These potential-transformers energize three rectifier-bridges Ba, B1, and Bo, which in turn energize three capacitors Ca, Cb and Cc, each ofwhich is paralleled by a separate resistor By. The voltage-drops in the three network-resistors Rr are applied, in three parallel circuits, across the output-terminals m and 12, through three reversely connected rectifiers (is, its and 60, respectively. The reverse-current or leakage-current through the rectifiers' is sufiicient to keep the output-terminals m and n energized, while the forward-current conductivity of the rectifiers 5a, ib and 5c is sufficient to pull.

down the uni-directional output-terminal voltage to the same value as the lowest of the three rectified line-voltages.

Since the minimum-voltage network just described has a fairly wide range of voltage-response, provided that no appreciable energy is taken from the output-conductors-m and n, I use a very high loading-resistance Roi. which is connected across. the output-terminals m and 'n of the minimum-voltage network, this loading resistance bein preferably comparable to. or larger than, the efiective reverse-current resistance of any one of the network-rectifiers 6a, (is or be. A suitable portion of the network voltage is tapped off of the loading-resistance ROI, as shown at l, and applied to the grid-control circuit of a triode tube 9, which has the two restraint-coils Filip. and FD2R connected in series with its plate-circuit, the plate-voltage being suppled by a resistor R02, which: serves as a potentiometer energized from a battery ID, or any other suitable directcurrent source.

The circuits of the several relays which are used in my invention are arranged, as far as practicable, after the manner of a schematic diagram or across-the-line diagram. In each case, the. main or operating coil' of the: relay is given a letter-designation or legend, and the same letter-designation or legend is applied to all of the contacts of that relay, The relays and switches areinvariably shown in their open or deenergized positions. Arrows are used to symbolically indicate how the various parts of each relay are connected together.

As shown in the Lensner et a1. application, the gas-filled tubes VI and V2 are controlled from the secondary winding 5 of the non-saturating transformerv NST, by having the tube-grids GI and G2 energized, through resistors RI and R2, from two secondary windings l l and !2 of an input-transformer IT, the primary of which is energized from the secondary winding 5 of the non-saturating transformer NST. The other two terminals of the secondary windings II and [2 of the input-transformer IT are'shown as being connected together, in a circuit l 4- which is connected to an intermediate tapped-point of a cathodecircuit biasing-resistor R31 which is in the cathode-circuits of the gas-tubes V! and V2.

As shown in the drawing, oneterminal of the minal 2| of thefirst, or carrier-starting, gas-tube- VI. The circuit I5 is also utilized to energize one terminal of another cathode-circuit loading-resistor R5, the other terminal of which is connected to the cathode-circuit 22 of the second, 01' relay-energizing, gas-tube V2.

The two grid-terminals of these tubes VI and V2 are connected to their respective cathode-circuits 2| and 22" through capacitors Cl and C2, as is known in the art. The two plate-circuits PI and P2 of these two tubes are connected together through a capacitor C3 which assists in firing-transfer. The two cathode-circuit loadingresistorsR t' and R5. respectively, are shunted by capacitors C4 and G5. which also assist in firingtransfer. The circuit HS, which is connected to an intermediate tap of the cathode-circuit biasingresi'stor R3, is also oonnected'to the circuits of the screen grids SGl and SGZ of the respective gastubes VI and V2. Thetwo plate or anode-circuits P! and P2 of the two gas-tubes are connected, respectively; through resistors R5 and R1, to a common conductor 24", which is in turn connected to the positive bus through a resistor R8.

The two alternately firing gas-tubes VI and V2 are supervised by the high-impedance or farreaehing fault-detector FDI, by having the positive tube-circuit 24 connected to the negat ve terminal through the normally closed backcontact 25 of said high-impedance fault-detector FDI.

The back-contact 25 of' the high-impedance fault-detector FDI is also utilized to control the energization of an auxiliary relay K, by having the operating-coil K of this auxiliary relay connected, through a resistor R9, across the FDI back-contact. The auxiliary relay K has a single back-contact K, which is connected in series with a telemetering key TM, which is indicated by way of illustration of carrier-current control for purposes other than relaying. The auxiliaryrelay back-contact K thus acts substantially like a back-contact placed upon the high-impedance fault-detector FDI, said auxiliary relay K being utilized for supplying this contact in order to avoid mechanically overloading the low-energy fault-detector FDI.

The cathode-circuits 2i and 22 of the respective gas-filled tubes VI and V2 are utilized as sources of two alternating series of square-topped positive-voltage impulses, for two different purposes. These positive-voltage impulses, are the voltage-drops through the respective cathode-circuit loading-resistors R4 and R5, which have voltage-drops therein when their respective tubes VI and V2 are firing.

The cathode-circuit 2| of the first gas tube VI is utilized to energize the plate-circuit P3 of a carrier-current master-oscillator tube OSC, through a radio frequency choke-coil RFC-l. This oscillator-tube OSC serves as a carrier-current transmitter for transmitting a succession of bursts of substantially square-topped, or unmodulated, carrier-frequency impulses to the other line-section terminal (not shown) as will be subsequently described. During fault-free conditions of the transmission-system, the gas-tubes VI and V2 are not firing, because of the short-circuiting backcontact FDI, and at such times the carrier-current oscillator OSC may be energized through the telemetering key TM, and the back-contact K, which connect the circuit 2| to the positive bus through a resistor RHl.

The transmitter-oscillator 080 has its screengrid SG3 connected to the plate-supply circuit 2! of said oscillator. The cathode-circuit of the oscillator 080 is the previously-mentioned circuit or conductor I5. The oscillator has a grid-circuit G3, which is connected to the cathode-circuit l5 through a grid-resistor R-l l.

The plate-circuit P3 of the oscillator OSC is A connected, through a blocking-capacitor BCI, to an intermediate terminal 21 of a tuned carrierfrequency circuit, comprising the conductor 21, a capacitor 06, a conductor 28, a capacitor C1, the cathode-circuit l5, a capacitor C8, the gridcircuit G3, and a variometer Ll, the other terminal of which is connected to the starting-point 2! of the tuned circuit.

The conductors 28 and G3 of this tuned circuit are respectively utilized to apply radioor carrierfrequency control-voltages, through blocking-capacitors BC2 and BC3, respectively, to the grids of two amplifier-tubes Al and A2. The cathodes of the amplifiers Al and A2 are connected to the cathode circuit I 5 of the oscillator 080. The grids of the amplifier-tubes Al and A2 are connected, through grid-resistors GRI and (5R2, to the negative bus so as to apply a negative bias equal to the drop across the cathode-circuit biasing-resistor R3. The two plates of the amplifiers Al and A2 are connected to the primarywinding terminals of a radio-frequency outputtransformer OT. The primary winding of said output-transformer OT has a midpoint tap 30 which is connected to the positive supply-terminal and also to the screen-grids of the two amplifiers A! and A2.

The radio-frequency output-transformer OT has a secondary winding 3|, having one of its terminals grounded, and having two taps 32 and iii 33. The output-transformer secondary-tap 32 is connected to phase-C of the line I, through a variometer L2, a conductor 34, and a couplercapacitor CC. The conductor 34 is also grounded through a grounding-coil GC. The secondary tap 33 of the radio-frequency output-transformer OT is utilized to energize the primary winding of a receiver-coupling transformer RCT, through a tuning-capacitor TC. The primary winding of the receiver-coupling transformer RCT is also preferably protected by a shunt-connected voltage-limiting gas-filled tube GT.

The receiving-coupler transformer RCT has a secondary winding 36 which is part of a tuned receiving-circuit, comprising said secondary winding 36, the grid-conductor G4 of a receivertube REC, a tuning-capacitor C9, the circuit or conductor l5, and thence back to the secondary winding 36.

The receiver-tube REC is a saturating-tube which carries a plate-cathode current which is of a substantially constant magnitude, whenever the tube is conducting at all, substantially regardless of the voltage applied to the grid-circuit G4, provided that this grid-voltage is high enough to cause plate-current to flow.

The receiver-tube REC has its cathode-circuit 3'! energized from a tapped point of a potentiometer P04 which is connected between the circuit [5 and the positive bus (-1-). The receiver-tube REC has a plate circuit P4, which is energized from the positive supply-terminal through a radio-frequency choke-coil RFC-2. In the drawing illustrative of my invention, I have symbolically shown the telemetering relays 38 in series with the plate-circuit P4, although it should be understood that, in general, the telemetering relays 38 would be utilized only at one line-terminal, while the telemetering key TM would be utilized at the other line-terminal. The receiverrelay REC also has a screen-grid circuit SG4 which is connected to the positive terminal The receiver-relay plate-circuit P4 is utilized to apply a restraining voltage to the grid-circuit G5 of a relay-tube RT, through a coupling-capacitor C-IB, a conductor 39, a voltage-doubler which is generically indicated at 40, and a gridcircuit resistor km. The voltage-doubler 40 consists of a resistor R-l3, which is connected between the conductor 39 and the cathode-circuit 22 of the second gas tube V2, a capacitor CH, which is connected between the circuit 39 and a circuit 4|, a double-circuit rectifier-valve RV, and a loading-resistor RI4. The loading-resistor RI4 is connected between the cathodecircuit 22 of the gas tube V2 and the anode-circuit 42 of the right-hand rectifier of the rectifiervalve RV. The circuit 42 also constitutes the input-terminal of the grid-circuit resistor Rr'l2 of the recever-tube RT. The cathode of the righthand half of the double-rectifier valve RV is connected. to the conductor 4|, while the anode of the left-hand rectifier-circuit of the doubler valve RV is connected to this same conductor. The cathode of the left-hand rectifier of the double valveRV is connected, at 43, to the cathode-circuit 22 of the second gas valve V2. The loadingresistor Rl4 is bypassed by a ripple-smoothing radio-frequency bypass-capacitor BPC.

The relay-tube RT has its cathode-circuit 44 enerized from a tapped point of a potentiometer POE which is connected between the conductor l5 and the positive supply-terminal The{ plate-circuit P5 of the relay-tube RT is connected through the primary winding of a relay output:

transformer ROT, a-conductor 45, a make-com. tact 46 ofthe low-impedance fault-detector FD2, and thenceto the positive terminal The screen grid circuit G5 of the relay-tube RT is alsouconnecteo. to the aforesaid conductor 45.

The relay output-transformer ROT has a secondary winding ll, which is used to energize the operating-coil R, of a relay R, which has a single make-contact 58, which is'shown, near the top of the negative supply-terminal as being in thetripping-circuit of the. trip-coil T0 of the circuit breaker 3, this trip-circuit extending from the negative bus to the positive bus and, also including the auxiliary breaker-contact 3d.

In operation, it; will be observed that my differential; fault-detectors FDI and FD2 have a distance-response which is not a measure of the. true impedance of the fault, yielding a sort of quasidmpedance. response. This is true, because the; operating-coil which is supplied by the current-network I-ICB is slightly different, for faults on different phase-conductors, and also for single ground-faults, double ground-faults, ungrounded 2-phase faults, and'3-phase. faults.

It is to be noted, however, that the balancepoints of both fault-detectors FDI and FD2 both shift at the same time and in the same direction, according to the. particular type of fault and the particular phase which is affected by the fault. Since. the two balance-points of the two faultdetectors both shift in the same direction, whenever the distance-setting of the relays. change, there will always be maintained a predetermined margin between the two distance-responses. In many applications of fault-detectors, and especially' in the particular fault-detector application which I have illustrated, in connection with a phase-comparing carrier-current protective system, the precise balance-point of a fault-detector is unimportant, because other means are provided for determining which fault to respond to, byway of a tripping-operation, but itis quite important that the relative sensitivities of two fault-detectors should be reliably maintained to all conditions. This function is admirably accomplished by my fault-detectors, because both detectors have a relay-restraint which is proportional to the minimum line-voltage, i. e., the line-voltage which has suffered the greatest voltage-drop under fault-conditions.

In some phase-sequence current-networks, such as the schematically indicated network HCB inmy. drawing, the network is more or less heavily weighted in response to the zero-sequence. line-current. component, so as to increase the sensitivity of responsiveness of the network to, ground-faults, as compared to phase-faults, because ground-faults commonly involve smaller ferrit -currents, than phase-faults. This oversensitive current-response to ground-faults is particularly useful, when used in combination with amim'mum-voltage network whichresponds to phase-'tgphase voltages, as distinguished from phase -'to-ground voltages. Because of the phase-- to-phase minimumwoltage-response, the particular minimum-voltage network which is illustrated in'thedrawin'gapplies a high restraint-voltage to the differential relays or quasi-impedance detectors FBI and FD2, in the case of phase-toground faults, because normally a phase-togrou'nd voltage should be applied to a groundfault impedance-relay. Since, however, my relay-FDl or FD2, in responding to ground-faults.

has too high a current and too high a. voltage applied thereto, these two discrepancies tend tocancel each other, causing the distance-response or reach of the relaysFDl and FD2 to be more nearly the same for phase-faults and ground faults.

The operation of the carrier-current part of the illustrated application of my invention will now be described. When a fault of a. predetermined severity occurs on the protected linesection I, one or both of the two fault-detectors FDI and FD2 will pick up. The high-impedance detector PD! is the more sensitive of the two,

andwhen it responds, it opensv its back-contact 25, andthus removes a short-circuit from around the two gas tubes VI and V2. The grid-circuit setting of these gas-tubes VI and V2 is such that said tubes are already in readiness to ture, in response to the alternating voltages which are applied to their respective grids G! and G2.

Whichever one of the two gas tubes Vi and V2 has a positive grid voltage applied to it, at the moment of opening of the FD! back-contact 25, will instantly begin firing, developing a certain positive voltage in its cathode-circuit Zlor 22, as the case may be, making said cathodecircuit positive with respect to the conductor !5. During the next half-cycle of the line-current, or output of the secondary winding 6 of the none saturating transformer NET, a positive gridvoltage is applied to the other one of the two. gas-tubes V! and V2, causing this other tube to fire, putting out the first-firing gas-tube, in the. process. The two gas-tubes Vi and V2 thus operate. as sources of two different series of flattopped voltageewa-ves of constant magnitude, one

gas tube being responsive to positive line-frequency half-cycles, while the other is responsive to negative line-frequency half-cycles.

Carrier-current is transmitted by the firing of the master-osci1lator-OSC during the flat-toppedvoltage-impulses which are supplied from the cathode-circuit 2| of the first gas-tube VI, thus. transmitting a succession of bursts of carriercurrent energy, which are applied to the line through the coupling capacitors CC, during linecurrent half-cycles of one polarity. During the line-current half-cycles of the other polarity, a.

positive. or operating-voltage is applied to the grid-circuit G5 of the relay-tube RT through the cathode-circuit 22 of the second gas-tube V2, the. voltage of the circuit 22 being applied to the gridcircuit G5 in series with the resistor R.!4, the.

conductor 42, and the resistor Rl2. This operating-voltage tends to cause the flow of platecurrent in the relay-tube RT.

The carrier-current impulses which are transmitted, from both ends of the protected linesection are received in the receiver-tube REC at each end of the line-section, but the only important received carrier-impulses, at either end, are. those which are received from the far end of the protected line-section, because the carriercurrent impulses, or bursts, or operating-periods, which are. transmitted from the relaying station itself, always occur during the half-cycles of the line-current when no operating-voltage is appliedto the grid-circuitGE of the relay-tube from the cathode-circuit- 722 of the second gas tube V2. At the far end of the protected line-section, however, the carrier-current energy-impulses or bursts, which are transmitted at line-frequency half-cycle intervals, are transmitted in response tothe cathode-circuit 2| of the'first gas tube VI in that station, so that, if the in-looking linecurrent at the far-end station is out of phase with the line-current at the relaying station (as it will be, when there is no fault in the protected line section), then the carrier-current transmitting-periods at the far end will exactly coincide with the operating-voltage half-cycle periods at the relaying station, and thus they will block a response of the relay-tube RT.

The received carrier-current energy is applied, in a blocking fashion, to the grid-circuit G5 of the relay tube RT, through the coupling capacitor -40 and the voltage-doubler 49, which operates to build up a negative voltage, in the loading resistor R|4, which is at least as large as, and opposite in sign to, the positive grid-voltage which is supplied by the cathode-circuit 22 of the second gas tube V2.

The result of the foregoing operations is that the relay-tube RT will become conducting only when there is an internal fault, or a fault within the protected line-section I, in which case the tube will become conducting periodically, in short or long bursts, depending upon the phase-relations between the line-currents at the opposite ends of the protected line-section. The alternating-current component of the plate-current of the relay-tube RT is applied to the operating coil of the phase-angle-responsive relay R, through the relay output-transformer HOT. The contact 53 of the relay R is then utilized to trip the breaker 3.

It will be noted that the carrier-current equipment acts as a pilot-channel connecting the two ends of the protected line-section for the purpose of effecting a determination or comparison of the phase-angle between the two terminal linecurrents of the protected line-section.

In order to insure the proper operation of the relay R, in view of its dependence upon faultresponsive relay-operations at two widely-separated points, namely at the two opposite ends of the protected line-section, it is necessary to make sure that the restraining impulses which are applied to the relay-tube RT are applied at least as soon as, and usually a trifle ahead of, the effective application of the operating-impulses to the grid-circuit G of this relay-tube RT. This coordination is obtained by using the second mechanical fault-detector F132 to supervise the tripping-circuit relay R, in response to the same derived fault-current which is utilized to energize the first fault-detector FDI; but the second fault-detector FD2 has a slightly higher current-setting, or lower impedance-setting, such as responding to a current-value of approximately 125% of the pick-up setting of the first faultdetector FDI, or an apparent impedance-value of approximately 80% (or any other fraction) of the pick-up setting of the first fault-detector FDI.

In the illustrated embodiment of my invention, I also make use of a back-contact 25 (rather than a, make-contact) on the first, or sensitive, faultdetector FDI, because a back-contact will not bounce, in response to a fault, thus avoiding the possibility of a momentary interruption of the transmission of a blocking or restraining signal at the beginning of a fault, thus resulting in false tripping at the opposite terminal. I also use a make-contact, 46, on the second fault-detector FDZ, so that, even though both of the fault-detectors should pick up simultaneously, the detector having the back-contact will get that contact open before the other detector has moved far enough to close a normally open make-contact, thus insuring that a restraining- Yoltage is available, on the relay-tube RT, a trifle ahead of the efiective application of an operating-voltage to the grid-circuit G5 of said relay tube it will be understood, of course, that no grid-circuit voltage is enective, on any tube, unless a suitable plate-voltage is being applied to the tube, so that the blocking of the operating voltage of the tube can be eiiected either by preventing the application of a suiiicientiy positive grid-voltage to the tube, or by preventing the application or a sufiicient plate-voltage to the tube.

w nile I have illustrated my invention, and de scribed its application, in but a single form of embodiment, which has been chosen for illustrative purposes, I wish it to be understood that many changes of addition, substitution or deletion could be made, without departing from the essential spirit of my invention. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

1. Terminal equipment for one terminal of a pilot-channel phase-angle relaying-system for a poiyphase line, comprising the combination, with a relay to be controlled, and a pilot-channel means for communicating with another terminal of the protected line-section, of means for deriving a single electrical current-responsive quantity from the polyphase line-current in such manner that the derived current-responsive quantity is responsive to a plurality of different kinds and severities of phaseand ground-iault conditions, means for deriving a single electrical voltage-responsive quantity from the several linevoltages in such manner that the derived voltage-responsive quantity is selectively responsive to the line-voltage having the greatest voltagedrop under fault-conditions, quasi-impedance fault-detector means, means for difierentially energizing said fault-detector means from said two derived quantities, line-current-responsive impulse-producing means, operating under the supervision of said fault-detector means, for applying a succession of operating-impulses, effeotive on said relay, in response to derived linecurrent half-cycles of one polarity, and for de-.- livering a succession of pilot-channel-controlling impulses to said pilot-channel means in response to derived line-current half-cycles of the opposite polarity, receiving-means for applying restraining-impulses, efiective on said relay, in response to pilot-channel impulses received from another terminal of the protected line-section, and means for supervising said relay in response to said fault detector means.

2. The invention as defined in claim 1, characterized by said operating-impulses, said pilotchannel-controlling impulses, and said restraining-impulses all being substantially flat-topped impulses of substantially constant magnitudes which are substantially independent of the faultseverity, the magnitude of the derived line-current or the magnitude of the received energy which is received over said pilot-channel.

3. Terminal equipment for one terminal of a pilot-channel phase-angle relaying-system for a polyphase line, comprising the combination, with a relay to be controlled, and a pilot-channel means for communicating with another terminal of the protected line-section, of an alternating current means for deriving a single-phase electrical current-responsive quantity from the polyphase line-current in such manner that the derived current-responsive quantity is responsive 11 to a plurality of different kinds and severities of phaseand ground-fault conditions, a means including a rectifier for deriving a unidirectional current-responsive quantity from said singlephase quantity, a minimum-voltage means, including rectifiers, for deriving a selected unidirectional voltage-responsivequantity from the several line-voltages in such manner that the selected quantity is responsive to the line-voltage having the greatest voltage-drop under faultconditions, quasi-impedance, polarized faultdetector means, means for differentially energizing. said fault-detector means from said two derived unidirectional quantities, line-currentresponsive impulse-producing means, operating under the supervision of said fault-detector means, forapplying a succession of operatingimpulses, effective on said relay, in response to derived alternating-current half-cycles of one polarity, and for delivering a succession of pilotchannel-controlling impulses to said pilotchannel means in response to derived alternating-current half-cycles of .the opposite polarity, receiving means for applying restraining-impulses, efiective on said relay, in response to pilot-channel impulses received from another terminal of the protected line-section, and means for supervising said relay in response to said fault-detector means.

4. The invention as defined in claim 3, characterized by said operating-impulses, said pilotchannel-controlling impulses, and said restraining-impuses all being substantially flat-topped impulses of substantially constant magnitudes which are substantially independent of the faultseverity, the magnitude of the derived linecurrent, or the magnitude of the received energy which is received over said pilot-channel.

5. Terminal equipment for one terminal of a pilot-channel phase-angle relaying-system for a polyphase line, comprising the combination, with a relay to be controlled, and a pilot-channel means for communicating withanother terminal of the protected line-section, of means for deriving a single electrical current-responsive quantity from the polyphase line-current in such manner that the derived current-responsive quantity is responsive to a plurality of different kinds and severities of phaseand ground-fault conditions, means for deriving a single electrical voltage-responsive quantity from the several line-voltages in such manner that the derived voltage-responsive quantity is selectively responsive to the line- .voltage having the greatest voltage-drop under fault conditions, two quasi-impedance fault detector means havingdiverse sensitivities, means for differentially energizing both of said faultdetector means from said two desired quantities, line current responsive impulse producing means, operating under the supervision of the far-reaching fault-detector means, for applying a succession of operating-impulses, eiiective on.

said relay, in response to derived line-current half-cycles of one polarity, and for delivering a succession of pilot-channel-controlling impulses to said pilot-channel means in response to derived line-current half-cycles of the opposite poiarity, receiving-means for applying restrainingimpulses, effective on said relay, in response to pilot-channel impulses received from another terminal of the protected line-section, and means for supervising said relay inresponse to the nearer-reaching fault-detector means.

6. The invention as defined in claim 5, characterized by said operating-impulses, said pilotchannel-controlling impulses, and said restraining-impulses all being substantially flat-topped impulses of substantially constant magnitudes which are substantially independent of the faultseverity, the magnitude of the derived line-current, or the magnitude of the received energy which is received over said pilot-channel.

7 The invention as defined in claim 6, characterized by the two fault-detector means being similarly operating mechanical relays, the more sensitive fault-detector relay having a normally closed contact, which opens when the relay responds to a fault, and the less sensitive faultdetector relay having a normally open contact, which closes when the relay responds to a fault, the fault-detector supervision which is specified in claim 9 being effected by said contacts, respectively.

8. Terminal equipment for one terminal of a pilot-channel phase-angle relaying-system for a polyphase line, comprising the combination, with a relay to be controlled, and a pilot-channel means for communicating with another terminal of the protected line-section, of an alternatingcurrent means for deriving a single-phase electrical current-responsive quantity from the polyphase line-current in such manner that the derived current-responsive quantity is responsive to a plurality of different kinds and severities of phaseand ground-fault conditions, a means including a rectifier for deriving a unidirectional current-responsive quantity from said singlephase quantity, a minimum-voltage means, including rectifiers, for deriving a selected unidirectional voltage-responsive quantity from the several line-voltages in such manner that the selected quantity is responsive to the line-voltage having the greatest voltage-drop under faultconditions, two quasi impedance, polarized, fault-detector means having diverse sensitivities, means for differentially energizing both of said fault-detector means from said two derived unidirectional quantities, line-current-responsive impulse-producing means, operating under the supervision of the far-reaching fault detector means, for applying a succession of operatingimpulses, effective on said relay, in response to derived alternating-current half-cycles of one polarity, and for delivering a succession of pilotchannel-controlling impulses to said pilot-channel means in response to derived alternatingcurrent half-cycles of the opposite polarity, receiving means for applying restraining-impulses. effective on said relay, in response to pilot-channel impulses received from another terminal of the protected line-section, and means for super vising said relay in response to the nearer-reaching fau t-detector means.

9. The inventionas defined in claim 8, characterized by said operating-impu ses, said pilotchannel-controlling impulses, and said restraining-impulses all being substantially flat-topped impulses of substantially constant magnitudes which are substantially independent of the faultseverity, the magn'tude of the'deriv'ed line-current, or the magnitude of the received energy which is received over said pilot-channel.

10. The invention as defined in claim 8,'characterized by the two fault-detector means being similarly operatingmechanical relays, the more sensitive fault-detector'relay having a normally closed contact, which opens when the relay responds to a fault, and the less sensitive faultdetector relay having a normally open contact,

13 14 which closes when the relay responds to a fault, UNITED STATES PATENTS the fault-detector supervision which is specified Number Name Date in claim 8 being effected by said contacts, respec- 2 144 494 Harder Jan 17 1939 tively- 2144499 Lenehar; Jan 17 1939 SHIRLEY GOLDSBOROUGH- 5 2,393,043 Harder Jan. 15,1946 2,406,584 Bostwick et a1. Aug. 27, 1946 REFERENCES CITED 2,408,868 Mehring et a1 Oct. 8, 1946 The following references are of record in the file of this patent: 

